Centrifuges are commonly used for fluid clarification in a wide variety of industrial applications such as grinding, honing, quench oils, thread rolling, vibratory finishing and many others. Some are manually cleaned when loaded with solids. Others discharge the collected solids automatically. Some automatically cleaned centrifuges discharge the solids as in the form of slurry along with a significant quantity of fluid. Others discharge the solids as a wet sludge.
There is a growing need, based on cost and environmental concerns, to produce solids in a dry or nearly dry state to facilitate disposal. Slurries, saturated solids, and loaded liquid filters pose significant handling and disposal problems.
Centrifuges designed to discharge nearly dry solids involve complicated and costly construction and high horsepower in order to accomplish their intended function. Decanter centrifuges involve a helix blade or blades that are geared to rotate at a speed slightly different than the bowl. This causes collected solids to be augured up a tapered portion of the bowl, called the beach, and out the open end of the bowl. The tapered portion of the bowl extends inside of the liquid surface. As solids move up the incline liquid is drained from the solids, which are discharged in a semi dry state. The decanter centrifuge has been proven practical in many material processing applications, but because of the complex design is too costly for many liquid clarifying applications.
Another class of centrifuges intended to discharge semi-dry solids incorporates an inclined blade positioned against the inside wall of a vertical bowl. To discharge collected solids, the rotating bowl is stopped and free liquid is allowed to drain from the bowl. A liquid collector is positioned under the bowl to catch the draining liquid. Once the liquid has drained this collector is withdrawn. The bowl is then held stationary while the blade is slowly rotated to plow the collected solids from the bowl inside wall and allow them to fall out the bottom of the bowl into a solids receptacle. The plowing process requires high forces to move the blade imbedded in the layer of solids. The plowed solids still contain a significant quantity of liquid and are wetter than desired in many applications making disposal more troublesome. This class of centrifuges has been successfully applied for a wide range of industrial applications. Because of wetness of the solids, and the complexity and cost of this class of centrifuges, they are impractical for many clarifying applications.